No abstract

We have proposed a novel method for the spectral irradiance measurement of the standard lamp. The measurement has been realized by using national primary scale based on a large area WC-C fixed point blackbody for the first time. The wavelength range is from 450 nm to 1000 nm. The spectral irradiance of the standard lamp has been measured based on the traditional variable temperature blackbody and large area WC-C fixed point blackbody. The results of the two methods agree within the uncertainties. Compared with the traditional measurement method, the fixed point method can reduce the major component of the spectral irradiance measurement uncertainty related to the temperature measurement.

This paper adopted an approximation of a melting plateau to solve the problem that temperature data cannot be monitored continuously when measuring the spectral irradiance of a large area tungsten carbide–carbon high-temperature fixed-point blackbody at each measured wavelength. Tests with fully measured curves showed that the method has a rather small deviation from the measured data of 0.017 K maximum, which corresponds to the spectral irradiance deviation of 0.005% at 500 nm. The maximum relative deviation between the Akima fitting method and the measured temperature in terms of spectral irradiance was 0.002%, which was better than − 0.067 % of a single temperature of 3020.11 K method and 0.026% of a linear interpolation method.

Spectral irradiance scale in the wavelength range from 250 nm to 2500 nm was realized at National Institute of Metrology (NIM) on the basis of a large area tungsten carbide–carbon (WC-C) high temperature fixed point blackbody, which is composed of a 14 mm diameter WC-C fixed point cell and a variable temperature blackbody BB3500MP as a furnace. A series of 1000 W FEL tungsten halogen lamps were used as transfer standards. The new spectral irradiance scale was compared with the scale based on a variable-temperature blackbody BB3500M, and the divergence between these two methods varied from -0.66% to 0.79% from 280 nm to 2100 nm. The measurement uncertainty of spectral irradiance scale based on fixed-point blackbody was analyzed, and the expanded uncertainty was estimated as 3.9% at 250 nm, 1.4% at 280 nm, 0.43 % at 400 nm, 0.27% at 800 nm, 0.25% at 1000 nm, 0.62% at 1500 nm, 0.76% at 2000 nm, and 2.4% at 2500 nm respectively. In the range from 300 nm to 1000 nm the fixed-point scale was improved obviously: the uncertainty decreased by more than 25% compared to the uncertainty based on the variable temperature blackbody. Below 300 nm, the uncertainty became higher because the signal to noise ratio was poor. Above 1100 nm, the contribution of temperature measurement to the uncertainty of spectral irradiance decreases, therefore the uncertainties of two methods are almost at the same level. The fixed-point blackbody was also used to realize the correlated colour temperature and distribution temperature of a tungsten filament lamp, the deviation from the variable temperature blackbody method was -0.5 K and -2.9 K, respectively.

No abstract